1. Field of the Invention
The present invention is directed to a lens grinding apparatus and more particularly to compact modular lens grinding apparatus for polishing and finishing of ophthalmic lenses.
2. Description of the Prior Art
Many apparatuses have been designed in the past for finishing ophthalmic lenses. In each case, a lap surface must be held in engagement with a lens surface while one or both move relative to the other in a preferred pseudo-random motion so as to smoothly finish the lens surface without causing ridges, grooves, and other aberrations on the lens surface.
The pseudo-random motion is often referred to as "break-up" motion. This motion may take a variety of forms as long as it does not change the polar alignment of the lens relative to the tool.
For example, U.S. Pat. No. 3,900,972, issued Aug. 26, 1975 to Rupp, attains this movement by coupling a polishing tool to an orbital driving means through a gimbal coupling designed such that the tool will be free to pivot about two perpendicular axes which are vertically displaced from one another relative to the lens and lap of tool surfaces. Specifically, one axis of the gimbal is spaced from the vertex of the tool surface by a distance equal to the radius of curvature of the tool surface in the direction of one principal meridian while the second axis is spaced from the vertex by a distance equal to the radius of curvature of the tool surface in the direction of the second principal meridian. Accordingly, as the tool in Rupp is orbitally driven, its lapping surface will automatically define and always move along a toroidal surface in space. The tool is mounted such that the orbital motion applied to it will continuously change in amplitude between upper and lower limits. This causes the tool to describe a spiral pattern relative to the lens surface which will insure that different parts of the tool will be contacting different parts of the lens at all times.
In U.S. Pat. No. 3,389,508, issued June 25, 1968 to Suddarth, et al., a lens blank supporting structure receives an orbiting movement while a "break-up" movement is provided by the lens lap. In U.S. Pat. No. 3,824,742, issued July 23, 1974 to Rupp, the tool is moved across the lens in a compound motion consisting of an oscillating movement in a first curve path having a radius equal to the radius of curvature desired in the direction of one major meridian of the surface coupled with a sweeping movement in a second curved path having a radius equal to the radius of curvature desired in the direction of the second major meridian of the surface. The tool is aligned relative to the lens surface such that the oscillating movement will be within a plane parallel to the tool axis such that substantially the entire abrasive surface of the tool will operate on the lens surface. In U.S. Pat. No. 3,892,092, issued July 1, 1975 to Keith, a first and second eccentric drive means are provided acting through one end of a drive arm which is movable both pivotally and axially and is connected at its outer end with a workpiece holder so as to move the workpiece through a multi-directional path over a flat horizontal polishing surface. One of the eccentric drive means imparts a relatively high speed circular motion to an inner end of the drive arm while the other drive means imparts a relatively low speed circular motion thereto, the composite of such motions providing the "break-up" motion desired. In U.S. Pat. No. 3,893,264, issued July 8, 1975 to Behnke, the polishing tool is moved through an orbit which describes substantially an ellipse while the lens is moved through an orbit which describes a circle in the same plane. Other prior art mechanisms for producing "break-up" movements are disclosed in U.S. Pat. No. 2,159,620 and U.S. Pat. No. 2,168,843.
Still another means for providing a "break-up" motion is disclosed in U.S. Pat. No. 3,732,647, issued May 15, 1973 to Stith. In Stith, the lens is moved laterally while the lapping tool is moved through a complex motion generated by two separate motors and a series of belts, eccentrics, and rods. While Stith in theory provides a satisfactory "break-up" motion, it requires careful alignment and adjustment at frequent periodical intervals.
Previous polishing machines share the common disadvantage of requiring many adjustments before being able to produce an acceptable finish on the workpiece. Furthermore, previous devices have a substantial number of components and are time consuming to service. Additionally, the previous machines which provide a good quality finish to a lens are fairly large, and therefore, take up a lot of space and are difficult to move.
What is needed, therefore, is a compact, modular, and easily serviceable lens polishing machine providing a high quality polished finish.